1. Field of the Invention
The instant invention relates generally to the field of LADAR (laser-radar) imaging technology. Specifically, the instant invention relates to a device which allows three-dimensional laser imaging of, for instance, partially obscured or camouflaged targets with very high range resolution and sensitivity.
2. Description of the Related Art
In general, existing LADAR imaging systems include a laser source, appropriate optics in conjunction with a detector array, processing circuitry suitable for processing the detector array output into a usable form and post-processing circuitry and software capable of taking the processed detector array output and converting it into a usable format such as an image on an electronic display.
Current LADAR imaging methods typically comprise scanning a target with a series of laser pulses and detecting the reflected photons (also referred to as a laser echo) with a photon detector array such as a focal plane array. The time measured between the initiation of each laser pulse and the return of the corresponding laser echo reflected from the target to the photon detectors on the array is used to calculate target range and to define surface features on a three-dimensional object. Such imaging capability is valuable in situations where, for instance, a vehicle is camouflaged or obscured by foliage or in an urban environment when an imaging sensor can acquire only a limited or angular view of a target.
Because the time of flight of the returning laser echoes will vary based on the distance between the detector array plane and the individual surface features from which the echoes are received, a three-dimensional image of a target can be assembled based upon the relative echo delays calculated from the corresponding outputs of the individual detectors in the array.
As an example, a laser echo delay between two laser echoes (traveling at about the speed of light) of one nano-second (10−9) suggests a target surface variation of about 15 centimeters. A similar laser echo delay of 500 picoseconds (10−12) between two laser echoes translates into a target surface variation of about eight centimeters.
As is evident from these short time periods, very high detector signal processing and timing circuit speeds are desirable in order to resolve target surface feature variations at a centimeter-level depth resolution. Unfortunately, existing LADAR imaging systems lack the necessary circuit speed and capacity to achieve very high (i.e., centimeter) range resolution and sensitivity.
Alternative prior art imaging means include conventional passive visible sensors, such as CCD video sensors, which provide easily interpreted information to an observer. Nonetheless, these types of sensors are undesirable where accurate scene information in a complex video environment (i.e., camouflaged or partially obscured targets) is an important factor in the observer's decision-making.
Accordingly, a need exists for a LADAR imaging system that has the circuit speed and density required to achieve range resolution and sensitivity necessary to define small target surface variations based on picosecond time of flight differences in laser echoes.
The instant invention addresses the aforementioned problems in prior art devices by providing a reliable, high speed, high circuit density LADAR detector system and device capable of providing range resolution and sensitivity at a centimeter level.